Modeling the Unsaturated Flow in Liquid Composite Molding Processes: A Review and Some Thoughts

Abstract

The liquid composite molding (LCM) processes for manufacturing polymer composites involve injecting a thermoset resin into a fiber-packed mold cavity. Very often, the fiber preform behind the resin front is partially saturated during the mold-filling process in LCM, giving rise to an unsaturated flow in that region. This paper first discusses the role of dual-scale porous media in inducing unsaturated flow in certain directional (woven, stitched, or braided) mats due to the delayed impregnation of tows. The approach of using a sink term in the mass balance equation is compared with the traditional approach of using unsaturated permeability for modeling unsaturated flow in dual-scale directional mats. Later, the relation of unsaturated flow with the phenomenon of bubble formation and migration is discussed. The lack of connection between the unsaturated flow research on the one hand, and the bubble creation and migration research on the other, is highlighted next. A few suggestions are offered on related topics, including the modeling of bubble motion, and the need for accurate experiments in unsaturated flow.

Unsaturated and Saturated Permeabilities of Fiber Reinforcement: Critics and Suggestions

“…In the literature, however, we can find a strong scatter of permeability measurement results even for a same fiber reinforcement, which depends on the measurement method (saturated permeability vs. unsaturated permeability), the test conditions (injection pressure or flow rate), and the test fluid (Dungun and Sastry, 2002;Pillai, 2004;Arbter et al, 2011;Naik et al, 2014;Vernet et al, 2014). To address this issue of inconsistency, there have been two benchmark exercises of permeability measurement (Arbter et al, 2011;Vernet et al, 2014).…”

“…• The ratio of unsaturated to saturated permeabilities varies from 1/4 to 4 (Dungun and Sastry, 2002;Pillai, 2004). In many cases, however, the unsaturated permeability is smaller than the saturated permeability (Dungun and Sastry, 2002;Pillai, 2004;Arbter et al, 2011;Naik et al, 2014;Vernet et al, 2014).…”

“…Currently, there is no standard method for permeability measurement and each laboratory uses its own experimental set-up and method. It has been reported that the experimental results for a same reinforcement can be different according to measurement method, device, and condition (Dungun and Sastry, 2002;Pillai, 2004;Arbter et al, 2011;Naik et al, 2014;Vernet et al, 2014).…”

Numerical prediction of saturation in dual scale fibrous reinforcements during Liquid Composite Molding

“…Many studies exist on void formation in LCM. A comprehensive review of these methods in [1] and [2] confirms the interest of understanding void creation mechanisms and transport in order to develop new optimisation strategies. Despite continual progress in the last decades, still many unresolved issues and limitations exist in current numerical approaches.…”

Simulación y control de los procesos de transferencia de resina en moldes flexibles mediante modelos de permeabilidad equivalente

“…Los valores de permeabilidad obtenidos en dispositivos saturados e insaturados pueden diferir debido al efecto de la capilaridad en flujos insaturados 76 . La impregnación de fibras secas en flujo insaturado está afectada por la presión capilar, la cual viene dada por la tensión superficial del fluido, el ángulo de contacto en la interfase fibra -fluido, que es afectada por el tratamiento superficial de las fibras 77 y el radio de las fibras 78 .…”